1. Field of the Invention
The present invention relates to fast electrical switching of high voltage circuits, and more particularly to silicon break over diode for such applications as pulse power switching and circuit protection.
2. Description of Related Art
The function of fast electrical switching of high voltage circuits is being done with various different types of semiconductor devices, including thyristors such as the gate turn-off thyristor (“GTO”), the super gate turn-off thyristor (“SGTO”), the light activated semiconductor switch (“LASS”), and the light triggered thyristor (“LTT”); insulated gate bipolar transistors (“IGBT's”); metal oxide semiconductor field effect transistors (“MOSFET's”), and a type of Russian device known as the dynistor.
Many of these devices have gates to control the functioning of the device. The gate turn-off thyristor, for example, has a gate electrode that is used along with anode shorts to control the turn-off of the device. However, the presence of additional terminals on a device increases the complexity of the control circuits for the device. In addition, the gate areas decrease the device active area, thereby reducing the current carrying ability of the device.
A type of device known as a break over diode (“BOD”), which is also known by the names reverse blocking diode thyristor (“RBDT”) and reverse switching rectifier (“RSR”), is a two-terminal thyristor having only an anode and a cathode. Advantageously, the device lacks a gate electrode. The RBDT, which has shorts to the cathode-base region, is capable of being switched from a high impedence “off” state to a low impedence “on” state in a very short period of time. RBDT's are disclosed in many publications, including Chang K. Chu et al, IEEE Industry Application Society, 1973, pages 267-82, and U.S. Pat. No. 4,076,555 issued Feb. 28, 1978 to Chang K. Chu et al. and entitled “Irradiation for Rapid Turn-Off Reverse Blocking Diode Thyristor.”
U.S. Pat. No. 4,080,620 issued Mar. 21, 1978 to Chang K. Chu and entitled “Reverse Switching Rectifier and Method for Making Same” discloses a reverse switching rectifier in which a PNPN semiconductor structure has an N-type end zone or cathode-emitter zone that penetrates to two different levels in the semiconductor body, namely a deep central portion and a shallow peripheral portion. The exposed surfaces of the N-type end zone are then metallized to provide electrical and thermal contact thereto. The patent further discloses a shunt pattern in the surface after the N-type diffusion of zones, in which each shunt has four nearest neighbors, a preferred center-center separation distance S being 20 mils, and a preferred diameter D being 5 mils. According to the patent, satisfactory results may be achieved with S in the range from about 10 to about 35 mils and D in the range from about 3 to about 11 mils, with larger diameters requiring a corresponding larger separation distance.
While RBDT's are used in various applications, they are not entirely well suited to very high power applications in excess of about 1.2 kV and 5 kA per part, or large current reversals for sustained periods of time. Moreover, they do not operate at close to theoretical blocking voltage.